Home Health Beating the heat
Illustrations by Stuart Briers
Illustrations by Stuart Briers

Beating the heat

Sweltering temperatures can make MS symptoms worse. Give them the cold shoulder with these sizzling ideas.

by Vicky Uhland

Bambi Lint’s family and friends often urge her to go outside and enjoy the fresh air on hot summer days. “They’ll say it’s just for a little while, but they don’t understand that even a little while can be too long,” says Lint, an Appleton, Wis., jewelry designer and gardener who was diagnosed with multiple sclerosis in 2001.

Lint started noticing problems with heat the first summer after she was diagnosed. “I was building a rock garden for one of my neighbors and the fatigue hit me like a brick. The heat caused so much spasticity and weakness in my legs that I just couldn’t go on anymore,” she says. “And it seems to have gotten worse every year. Now, if I’m outside and the sun is pounding on me and it’s warmer than 75 degrees, I can’t last more than 15 minutes.”

Heat intolerance is such a pervasive symptom in people with MS that the “hot bath” test used to be one of the main ways of diagnosing the disease. In the l9th and early 20th centuries, doctors immersed people whom they suspected had MS in water that was around 105 to 110 degrees. If neurologic symptoms appeared or worsened, the doctor concluded that the patient did indeed have the disease.

With the advent of magnetic resonance imaging, spinal taps and other modern-day diagnostic tools, the hot-bath test has become an antiquated anecdote. But that doesn’t mean that heat sensitivity is any less of an issue. Researchers estimate that 60 to 80 percent of people with MS have a temporary worsening of their symptoms when they become overheated. In a 2004 international survey of more than 2,500 people with MS, 70 percent reported that heat worsened their MS symptoms. And a 2011 Swedish study of 265 people with MS found that 58 percent had heat sensitivity that significantly increased their fatigue, pain, concentration or urination urgency.

Raising the thermostat

Known as Uhthoff’s phenomenon, after the physician who first discovered it in 1889, heat sensitivity affects people with MS and other demyelinating diseases. Basically, says Teresa Frohman, PA-C, who co-authored a 2013 paper published in Nature Reviews Neurology on Uhthoff’s phenomenon, as little as a half-degree increase in body temperature makes it harder for nerve impulses to operate normally. “Heat changes the amount of energy the body needs to keep the nerve impulses going,” she says.

This in turn creates pseudoexacerbation—a temporary worsening of physical and cognitive symptoms. So people who experience weakness, fatigue, balance issues, spasticity, blurred vision, concentration problems, memory difficulties or other MS symptoms are likely to feel them more acutely if their body temperature is raised, whether due to heat, exercise, fever, infection, or even psychological stress or, for women, menstruation.

The good news is that a pseudoexacerbation is not the same as a relapse and disappears once the body’s temperature reverts to normal. “It’s usually very short in duration—less than 24 hours—and totally reversible,” says Frohman, who is a clinical specialist at the Multiple Sclerosis Clinic at the University of Texas Southwestern and co-author of the National MS Society’s book, Multiple Sclerosis for the Physician Assistant.

But knowing that it’s not permanent doesn’t make a pseudoexacerbation any less real or distressing when it’s happening. “I may be feeling great, and then I go outside in the heat and do some planting in the garden, and bam! I can hardly move,” Lint says. “The heat exacerbates the fatigue and other symptoms and nearly incapacitates me. One of the most frustrating parts is there are no warning signs. What I could tolerate yesterday, may or may not be the same as what I can tolerate today.”

Understanding the thermostat

Evidence suggests that heat sensitivity becomes more common as the disease progresses, but researchers aren’t sure why some people with MS are relatively unaffected by hot temperatures. And while many people with MS report that the old adage “it’s not the heat; it’s the humidity” is particularly true for them, Frohman says there’s no scientific evidence that high humidity exacerbates MS symptoms more than high heat. It is true, however, that when humidity is high, sweat does not evaporate as efficiently, so it has less of an ability to cool the body. So people may perceive that their symptoms are worse.

Frohman says people with MS may be particularly affected by heat because they tend to have resting body temperatures that are lower than the usual 98.6 degrees. “In our patient population of over 5,000, we’ve discovered that the average temperature is 96.9 to 97.5 degrees, so someone presenting at 99 degrees could actually have a fever,” she says. A 2010 paper published in the Journal of Applied Physiology reported that this may be because MS affects areas of the brain and nervous system that regulate core body temperature.

This faulty internal thermostat may also affect the body’s sweat glands, according to the study. The researchers found that people with MS don’t tend to perspire as much as the rest of the population, which can lead to overheating because sweat helps the body cool itself. In addition, the researchers noted that people with MS-related bladder problems may restrict how much they drink, which also reduces sweating.

Certain treatments can increase or decrease heat sensitivity as well. People who take anticholinergic medications—a specific type of treatment sometimes used for bladder issues in MS—may have reduced sweating, Frohman says. Conversely, potassium-channel blockers such as 4-aminopyridine, or 4-AP, which are taken for relief of many MS symptoms, may improve heat-related fatigue or cognition problems.Frohman says she and her colleagues have found that Ampyra, a type of 4-AP approved by the Food and Drug Administration for gait-related issues, is also effective for Uhthoff’s phenomenon, although it’s not specifically approved for that use.

Tags: Summer 2014